Ultrafast absorption studies on free‐standing porous silicon films have been carried out at room temperature to investigate the carrier dynamics and the luminescence mechanism. Ultraviolet and visible excitations were used on an as‐prepared sample and two annealed samples. Transient absorption curves of UV pumped, as‐prepared samples contain a fast decay (&tgr;f) of 0.8±0.2 ps and a slower decay of ≳30 ps. &tgr;fis found to be shorter for both the 500 °C annealed sample with UV excitation and for the as‐prepared sample with visible excitation. The faster decay rates suggest that the subpicosecond component of the transient absorption may be due to carrier thermalization rather than core‐to‐surface state excitation transfer. ©1995 American Institute of Physics.